The present invention is directed to a housing for a fast exhaust sensor for a cylinder-selective lambda measurement in an internal combustion engine. The housing has a hollow cylindrical form and has at least two slot shaped openings which are arranged rotational symmetrical over its circumference and lie parallel to the axis of the hollow cylindrical housing with the edges overlapping in a fashion of a venetian blind.
What is referred to as a fast exhaust gas sensor shall be advantageously utilized in the future for cylinder-selective lambda control. A sensor effect of these fast exhaust gas sensors is based on the gas sensitivity of the electrical conductivity of certain semiconductor metal oxides. Up to now, the lambda control occurs with what was referred to as a slow sensors that are only in the position to adequately detect stationary operation. It will be possible to also control the non stationary operating conditions of an internal combustion engine with the anticipated, new probes. The preferred gas sensitive materials are either strontium titanate or cerium oxide. In order to achieve an adequate high response speed, these gas sensitive metal oxides are to be applied to the substrate of the sensor as either a thin film or as a thick film.
As known, the exhaust gas of internal combustion engines is loaded with particles. These particles occur from the additives and from the impurities of the fuel supplies such as lubricating oil, benzene, etc. and due to abrasion of motor parts. The particles have a typical size of 1 through 2 micrometers and are composed among other things, of iron oxide. The deposited particle layer has a considerable electrical conductivity. Solid deposits will short circuit the sensor layer given either the thick film or thin film sensors. Even a slight deposit of these particles on the gas sensitive element of the sensor changes the gas-sensitive and electrical properties thereof and will lead to a degradation so that the desired useful life of the sensor cannot be achieved.
Exhaust gas sensors having a gas-sensitive thin films are previously unknown. The known electrochemical or resistive exhaust gas sensors are executed as a bulk ceramic or as thick film sensors. They are considerably less sensitive to contamination due to the particles but do not achieve the high response speeds required for a cylinder-selective lambda measurement. In order to prevent solid deposits, the "viewing openings" of the sensor are kept as small as possible and the sensor is coated with an inert, porous protective layer. Since slight deposits do not deteriorate the sensor function, no particular value is attached to an optimum flow-through of the housing and to keeping the particles entirely away in the known solutions.